1. Field of the Invention
The present invention relates generally to systems for inspecting the interior of pipes and other conduits or voids, and more specifically to the design of push-cables used to move an inspection camera into pipes, conduits or other hard-to-access areas.
2. Description of the Related Art
There are many situations where it is desirable to internally inspect long lengths of pipe that are already in place, either underground, in a building, or underwater. For example, sewer and drain pipes frequently must be internally inspected to diagnose any existing problems and to determine if there are any breaks causing leakage or obstructions impairing the free flow of waste. It is also important to internally inspect steam pipes, heat exchanger pipes, water pipes, gas pipes, electrical conduits, and fiber optic conduits for similar reasons. Frequently, pipes that are to be internally inspected have an internal diameter of six inches or less, and these pipes may make sharp turns. It is sometimes necessary to internally inspect several hundred feet of pipe. The capability to inspect smaller diameters such as bathroom drains and small voids such as the interior of walls or other construction areas is highly desirable and is constrained by the performance and specifications of the push-cable used as well as the design of the camera head and its connections.
Video pipe inspection systems have been developed that include a video camera head that is forced down the pipe to display the pipe interior on a video display. The inspection is commonly recorded using a video recorder (VCR) or digital video recorder (DVR). Conventional video pipe inspection systems have included a semi-rigid push-cable that provides an electromechanical connection between the ruggedized camera head that encloses and protects the video camera and a rotatable push reel used to pay out cable and force the camera head down the pipe. The inspection push-cable must be specially designed to be flexible enough to make tight turns yet rigid enough to be pushed hundreds of feet down small diameter pipe. The push-cable needs to incorporate electrically conductive cable having the proper conductors and impedance for conveying the NTSC or other video signals to the video display unit and for coupling to external power and ground conductors. Examples of suitable video push-cables are disclosed in U.S. Pat. No. 5,457,288 issued Oct. 10, 1995 to Mark S. Olsson and U.S. Pat. No. 5,808,239 issued Sep. 15, 1998, to Mark S. Olsson. The video camera head design and the manner in which it is connected to the distal end of the video push-cable are important to the performance and reliability of a video pipe inspection system. These structures must be rugged, yet the camera head must be compact and its manner of connection to the video push-cable flexible enough to bend through tight turns. Existing designs typically require an electrical termination at the rear end of a protective flexible spring extending from the camera head and shielding parts from abrasion while also serving to lead the push-cable around curves in the pipe or other space under inspection.
Conventional push-cables used for such inspections are often helically wrapped with filler rods and conductors wound around a semi-rigid central push-rod. The central push-rod is typically a high-strength rod of composite material, which provides the stiffness necessary to push the cable a considerable distance. The limitations of flexure of the central push-rod makes the push-cable suitable for traversing turns on the order of ninety degrees in drain pipes of a diameter on the order of four to six inches. As the pipe diameter decreases or the angle of required turns increases, the central push-rod reaches the limits of its performance. A conventional push-cable with a semi-rigid central push-rod also has the drawback of a single mode of failure in the central push-rod if it is over-stressed by too narrow a bend, for example. A need is strongly felt in the field for a push-cable capable of robustly managing tighter turns and smaller diameter pipes and openings.